I like Snowmass, but I much prefer to stay in Aspen. Snowmass is bigger than the other 3 combined. It's a little more Deer Valet than the others, but Hanging Garden and the Headwall are steep enough to make me pay attention. Snowmass has everything except the steepest terrain, like Highland Bowl or the Ajax backcountry.
The bus system works fine if you stay in town, The free bus stops at 5 or 6 pm, but Snowmass bartenders will give you a voucher if you stay late. I never stayed in Snowmass, so I can't comment on how the buses work if you stay there, but I assume they work work both ways equally well.
One day each at Snowmass, Highlands and Ajax sounds like a good plan. You'll have a good time regardless of where you stay. The best lunch is pineapple cheeseburgers at Gwynn's at Snowmass. Bentley's is my favorite bar in Aspen. There's more good things there than you can do in 3 days.